If both terms are meant to be small piles with dimension not more than 300mm in diameter then both can be considered to be in the same category.
Mini piles are of may types from being made of concrete, wood or steel and can be install in many ways too. They can be hammered in, pushed in and even screwed in too. However they can also be installed by drilling and grouting. Thus in this situation mini piles can be grouped with micropiles.
The micropiles in this site are installed by drilling and grouting using cement grout and normally will have a center reinforced with a metal core that can be made up of steel bars to API pipes.
In term of performance, micropiles have greater load capacity and lateral resistance compared to the other mini piles. Micropiles can also be used to resist tension loads and this is where other types of mini piles can’t match.
As in this post “common use of micropiles” the usage of micropiles are many and also it can be changed or modify to suit conditions on site.
Then when it comes to the installation of micropiles, this has become more or less a specialist job. The equipment are specialize and drillers or the rigs operators required experience. It is not just anyone can just decide to become a micropiles specialist without any previous experiences.
Thus to conclude, mini piles and micropiles are the same as far as size/dimension is concerned. And if they are installed by drilling and grouting mini piles are the same as micropiles.
However if they are install otherwise, the similarity ends there. There are differences when it comes to performances where in most cases micropiles are much superior ( author personal opinion) . However having said that, this cannot be apply across the board as there are other consideration to be taken into account too. These include costs, construction timetable, availability of equipment and the types of project.